A negative type photosensitive material which employs photopolymerization or photocrosslinking reaction has been used for a wide variety of applications, such as photoresist, ink, printing and the like.
In letterpress printing technique, particularly for newspapers, an automatic platemaking system has been widely introduced to speed up platemaking. In this system, for example, a piece of photosensitive resin plates is lifted with suckers from a stack of photosensitive resin plates and moved to an exposing stage. The resin plate is therefore required to have good dimensional stability.
It is also preferred that the photosensitive resin plate is developed with water rather than organic solvent or alkali aqueous solution, in view of labor's health, safety and environmental pollution. Furthermore, it is also preferred the proposed plate has good durability against ink, especially aqueous ink and emulsion ink.
In order to satisfy the above mentioned requirements, some improvements are proposed in U.S. Pat. No. 3,801,328 and Japanese Kokai Publication (unexamined) 22339/1986. The printing plate obtained from the U.S. Patent, however, is poor in durability against ink. The photosensitive resin plate of the Japanese Publication has good water developing ability, but it is poor in dimensional stability and is not suitable for the automatic platemaking system. The obtained printing plate from the Japanese Publication has good durability against ink, but it has tacky surface, which causes building up of ink on the surface. Accordingly, the printing plate has to be often washed while printing. The printing plate also has low hardness and elasticity, which causes dot gain.